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Ítem Study of APS and conventional sintering parameters for the manufacture of TiO2 targets for PAPVD(IOP PUBLISHING LTD, 2019-01-01) Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In surface science of functional oxides, titanium dioxide (TiO2) is one of the most investigated crystalline systems either in rutile or anatase phases. In this work commercial TiO2 powders are used to study the required process conditions to obtain TiO2 targets by Atmospheric Plasma Spray (APS) and conventional sintering, with suitable physical and chemical properties to be source material for Plasma Assisted Physical Vapor Deposition (PAPVD) for technological and medical applications. Two three factor Box Behnken experimental designs combined with surface modeling were employed to estimate the influence of spraying parameters (gun current, Ar/H2 ratio and standoff distance) and sintering parameters (heating rate, sintering temperature and holding time) within the targets microstructure (cracks and pores in cross section) and phases composition. The microstructure and composition of APS-deposited targets and sintered ones were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The lowest defects percentages of the targets manufactured in this work were 0.41 ± 0.30 % for APS-deposited targets and 0.05 ± 0.04 % for the sintered ones using the optimal parameters suggested by the statistical model, which allowed confirming the advantages of sintering process and limitations of APS in terms of microstructural homogeneity, but also of the use of design of experiments in the modeling of systems of many variables when there is not diagnostic equipment of the processes available. © Published under licence by IOP Publishing Ltd.Ítem Green synthesis of magnetic nanoparticles using leaf extracts of Aloe vera and Kalanchoe daigremontiana to remove divalent mercury from natural waters(IOP PUBLISHING LTD, 2019-01-01) Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In this study, magnetic nanoparticles of magnetite were prepared by an eco-friendly method using aqueous leaf extracts of Aloe vera and Kalanchoe daigremontiana. These vegetal extracts have suitable characteristics such as high availability, low cost, and serve as good colloidal stabilizers. Synthetized products were characterized by Transmission Electron Microscopy (TEM), Room Temperature Mossbauer Spectroscopy (RT-MS), and their potential use as adsorbents for Hg (II) removal in natural waters was evaluated by Atomic Absorption Spectroscopy (AAS). Size distribution and morphology of the products obtained by TEM show spherical nanoparticles composites, with sizes between 3 and 10 nm for both extracts. Mossbauer spectra are consistent with superparamagnetic particles for both samples. Moreover, particles from both extracts showed mercury removal efficiencies above 75%. © Published under licence by IOP Publishing Ltd.Ítem Modeling, simulation and test of the heat flow in a liquid nitrogen cryostat for Mössbauer spectroscopy(IOP PUBLISHING LTD, 2019-01-01) Gutiérrez N.A.; Velásquez A.A.; Gutiérrez N.A.; Velásquez A.A.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In this work, we present a heat flow analysis for a conceptual design of an open cycle liquid nitrogen cryostat with application in Mössbauer spectroscopy. Initially, we made a study of the different configurations of Dewar type cryostats reported in the literature. These configurations are based on existing designs and the Mössbauer spectrometer requirements of the Instrumentation and Spectroscopy Laboratory at Universidad EAFIT in Medellin. From this study, we establish our own conceptual design. A first heat flow analysis in stationary state was calculated to obtain the dimensions of the reservoir vessel. The heat flow model obtained predicted an adequate evaporation time of the liquid nitrogen for the acquisition of Mössbauer spectra. For this model we employed the Fourier's law, the heat flow by radiation in grey bodies and the properties of 304 stainless steel, 6061 aluminium alloy and OFHC copper. In consequence, the mechanical design of the cryostat was defined and the new heat loads associated with it were added to the initial model. Finally, the prototype was built, the model was tested and some final corrections were made. © Published under licence by IOP Publishing Ltd.Ítem Characterization of the corrosion products of one of the pedestrian paths of the bridge "punto Cero" in the city of Medellin, Colombia(IOP PUBLISHING LTD, 2019-01-01) Velásquez A.A.; Jaramillo Raquejo D.; Velásquez A.A.; Jaramillo Raquejo D.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In this work, we present the structural and magnetic characterization of the rust products formed on one of the pedestrian paths of the bridge "Punto Cero" of the city of Medellin, Colombia. The rust products were obtained by scraping three zones of the surface of the pedestrian path, namely: a surface that faces the sky, a surface that faces the floor of the path and a surface with a crack, where a high corrosion state was observed. The rusts were characterized by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, room temperature Mössbauer Spectroscopy and Vibrating Sample Magnetometry. The analyses made by these techniques show that the rust products formed on the surfaces facing the sky and floor are composed mainly by goethite, lepidocrocite and maghemite, in percentages of 74%, 24% and 2% respectively, while the rust taken from the more corroded substrate presented 55% of goethite, 28% of lepidocrocite and 17% maghemite. Mössbauer and X-ray measurements were highly consistent with the percentages of each phase found in all rusts. The results suggest that in addition to the type of steel and the atmospheric conditions which the structure is exposed, the specific location of some surfaces plays an important role in the type and percentage of phase formed on them, being higher the presence of spinel phase in the zones more prone to moisture accumulation. On the other hand, the formation of maghemite could be an indication of an important state of corrosion of some surfaces, which could serve as a guide to start preventive maintenance actions on the structure. © Published under licence by IOP Publishing Ltd.Ítem HIPAE helicopter-borne in-situ pollution assessment experiment: Plataforma alternativa para la medición de contaminantes en capas verticales(Institute of Electrical and Electronics Engineers Inc., 2019-01-01) Botero A.Y.; Florez J.; Duque J.F.; Rendon A.; Lopez-Restrepo S.; Pinel N.; Quintero O.L.; Oquinte1@eafit.edu.co; Rodriguez J.S.; Galvez J.; Lopera D.V.; Montilla E.; Marulanda J.I.; Isaza C.; Lainez M.L.A.; Zapata A.F.; Botero A.Y.; Florez J.; Duque J.F.; Rendon A.; Lopez-Restrepo S.; Pinel N.; Quintero O.L.; Oquinte1@eafit.edu.co; Rodriguez J.S.; Galvez J.; Lopera D.V.; Montilla E.; Marulanda J.I.; Isaza C.; Lainez M.L.A.; Zapata A.F.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)[No abstract available]Ítem Optical design of a high-power LED-based solar simulator(SPIE-INT SOC OPTICAL ENGINEERING, 2016-01-01) Toro, Veronica; Velasquez, Alejandro; Velásquez, D.; Acevedo, David Felipe; Toro, Veronica; Velasquez, Alejandro; Velásquez, D.; Acevedo, David Felipe; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)The optical design of a High-Power LED based Solar Simulator was made in order to reach the AM1.5G spectrum standards. An optical model of the light emitted by the LEDs was made and used for spectral intensities calculations and the light intensity uniformity was optimized. A class AAA solar simulator was designed using a hexagonal LED distribution.Ítem Synthesis of Alumina Thin Films Using Reactive Magnetron Sputtering Method(IOP PUBLISHING LTD, 2017-06-13) Angarita G.; Palacio C.; Trujillo M.; Arroyave M.; Angarita G.; Palacio C.; Trujillo M.; Arroyave M.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)Alumina (Al2O3) thin films were deposited on Si (100) by Magnetron Sputtering in reactive conditions between an aluminium target and oxygen 99.99% pure. The plasma was formed employing Argon with an R.F power of 100 W, the dwelling time was 3 hours. 4 samples were produced with temperatures between 350 and 400 °C in the substrate by using an oxygen flow of 2 and 8 sccm, the remaining parameters of the process were fixed. The coatings and substrates were characterized using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) in order to compare their properties before and after deposition. The films thicknesses were between 47 and 70 nm. The results show that at high oxygen flow the alumina structure prevails in the coatings while at lower oxygen flow only aluminum is deposited in the coatings. It was shown that the temperature increases grain size and roughness while decreasing the thicknesses of the coatings. © Published under licence by IOP Publishing Ltd.Ítem Analysis of chemical processes for the synthesis of magnetite for biomedical applications(IOP PUBLISHING LTD, 2011-01-01) Baena, J.; Marulanda, J.I.; Baena, J.; Marulanda, J.I.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)This article demonstrates the evaluation of wet chemical routes to produce magnetic nanoparticles of iron oxide and surface chemistry characterization by infrared spectroscopy (IR). Its potential use in biomedicine as contrast agents or to deliver drugs in localized medical treatments, which reduce the toxicity associated with cytotoxic drugs, is also evaluated.Ítem Comparison of TiO2 targets manufactured by APS and sintering processes for PAPVD coatings suitable in technological and medical applications(ASM International, 2018-01-01) Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Jaramillo Raquejo D.; Palacio C.C.; Ageorges H.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In surface science of functional oxides, Titanium dioxide (TiO2) is one of the most investigated crystalline systems either in rutile or anatase phases. Rutile phase is widely used in microelectronic, tribological applications and in the conversion of solar energy. Anatase phase is used in self-cleaning, antifogging, photo-catalytic and biomedical technologies. This work focuses on studying the required process conditions to obtain TiO2 targets by APS onto metallic substrates using commercial TiO2 powders (Oerlikon Metco in Switzerland) with suitable physical and chemical properties for technological and medical applications as PAPVD coatings. APS targets were compared to sintered ones. The raw powders were characterized by laser diffraction, SEM, XRF and XRD while the characteristics of the APS-deposited targets as well as the sintered ones were determined by SEM and XRD to identify the constituent phases. This work allowed confirming the advantages and limitations of both processes in terms of grain size, chemical composition, microstructural homogeneity and density in order to choose the best option to manufacture targets for PAPVD coatings for technological and medical applications. © 2018 ASM International® All rights reserved.Ítem Study of the suitability of a commercial hydroxyapatite powder to obtain sintered compacts for medical applications(IOP PUBLISHING LTD, 2017-06-13) Palacio C.; Jaramillo D.; Correa S.; Arroyave M.; Palacio C.; Jaramillo D.; Correa S.; Arroyave M.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)Hydroxyapatite (HA) is a material widely used by the medical community due to its Ca/P ratio is comparable to the Ca/P ratio of bones and teeth, which promotes osteoinduction and osteoconduction processes when in contact with bone tissue, either as volume piece or coating. This work focuses on studying the quality of the commercial HA powder MKnano-#MKN-HXAP-S12 µm, after processing, to obtain sintered compact discs with suitable physical and chemical characteristics for implants applications. The HA powder was processed through calcination, grinding, pressing and sintering to evaluate the effect of such as procedures in the compacts dics quality. The raw powder was characterized by laser diffraction, SEM, XRF, XRD, TGA and DSC while the characteristics of the obtained compact discs were determined by dilatometry and XRD to identify the sintering temperature range, constituent phases, the amorphous content and the crystallinity degree, parameters that allow determining their suitability for implants applications. Although, it was not possible to obtain sintered compacts with the suitable chemical composition and without fractures, this work allowed to identify the parameters that determine the suitability of a HA powder to obtain sintered compacts for medical applications, as well as the characterization protocol that allows the evaluation of such parameters. © Published under licence by IOP Publishing Ltd.Ítem Solution of the wave equation for an oscillating punctual source by means of the finite elements method(SPIE-INT SOC OPTICAL ENGINEERING, 2016-01-01) Marín-Suárez, M.; Marín-Suárez, M.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)Finite Elements Method (FEM) and Finite Differences Method (FDM) in the Euler implicit approach, were used in order to determine the bi-dimensional electromagnetic field of an oscillating punctual source inside a square geometry with three reflective boundaries and an absorbing one. Although the main approach consist in solving the wave equation for the electric field, it was decided to use the approach of electromagnetic potentials V and A because those potentials give a simpler solution for both, the electric and magnetic fields. Besides, a comparison with theory was made, solving for an electromagnetic field without boundaries produced by an oscillating punctual source.Ítem Low-cost detection of RC-IED activation signals in VHF band(SPIE-INT SOC OPTICAL ENGINEERING, 2014-01-01) Camargo Suarez, V.H.; Marulanda B., J.I.; Camargo Suarez, V.H.; Marulanda B., J.I.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)The proliferation of Radio Controlled Improvised Explosive Devices (RC-IED) is a growing threat around the world. The ease of construction and low cost of these devices are transforming common things in lethal tramps. The fight against this threats normally involves the use of sophisticated and expensive equipment of Electronic Warfare based on high speed DSP systems, just to detect the presence of detonation signals. In this work is showed how to find activation signals based on the characteristic of the power in a specific band and the previous knowledge about the detonation signals. As proof of concept we have taken the information about the RC-IEDs used in the Colombian conflict and develop an algorithm to find detonation signals based on the measured power in frequencies between 136 MHz and 174 MHz (2 meter civil band). © 2014 SPIE.4.Ítem Gunshot identification system by integration of open source consumer electronics(SPIE-INT SOC OPTICAL ENGINEERING, 2014-01-01) López R., J.M.; Marulanda B., J.I.; López R., J.M.; Marulanda B., J.I.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)This work presents a prototype of low-cost gunshots identification system that uses consumer electronics in order to ensure the existence of gunshots and then classify it according to a previously established database. The implementation of this tool in the urban areas is to set records that support the forensics, hence improving law enforcement also on developing countries. An analysis of its effectiveness is presented in comparison with theoretical results obtained with numerical simulations. © 2014 SPIE.Ítem Low-cost localization system of impulsive sounds for urban environments(SPIE-INT SOC OPTICAL ENGINEERING, 2014-01-01) López R., J.M.; Marulanda B., J.I.; López R., J.M.; Marulanda B., J.I.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)A low-cost acoustic localization system is presented, in which a video camera is directed towards the source of impulsive sounds such as gunshots. An analog filter is implemented at the first stage, in order to reduce the range of frequencies to analyze, hence narrowing and improving the localization of gunshots. The system is design for the integration of open source consumer electronics and processing devices, which makes large-scale deployment possible even in developing countries. Furthermore, results are also obtained with a prototype that shows a high percentage of successes.. © 2014 SPIE.Ítem Analysis of a developed analog trilateration system of impulsive sounds(SPIE-INT SOC OPTICAL ENGINEERING, 2014-01-01) López R., J.M.; Marulanda B., J.I.; López R., J.M.; Marulanda B., J.I.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)A characterization study is made from a trilateration system for impulsive sounds, in which theoretical analysis and experimental results are presented. This system uses an analog trilateration method, avoiding to implement high frequency ADC conversion elements. It also presents the optimization of the chosen array of microphones, thus allowing for a better trilateration algorithm behavior. © 2014 SPIE.Ítem Distributed admission control without knowledge of the capacity region(IEEE, 2013-01-01) Jose Jaramillo, Juan; Ying, Lei; Jose Jaramillo, Juan; Ying, Lei; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)We consider the problem of distributed admission control without knowledge of the capacity region in single-hop wireless networks, for flows that require a pre-specified bandwidth from the network. We present an optimization framework that allows us to design a scheduler and resource allocator, and by properly choosing a suitable utility function in the resource allocator, we prove that existing flows can be served with a pre-specified bandwidth, while the link requesting admission can determine the largest rate that it can get such that it does not interfere with the allocation to the existing flows. © 2013 IEEE.Ítem Comparative studies of the feed gas composition effects on the characteristics of DLC films deposited by magnetron sputtering(ELSEVIER SCIENCE SA, 2004-07-01) Libardi, J.; Grigorov, K.; Massi, M.; Otani, C.; Ravagnani, S.P.; Maciel, H.S.; Guerino, M.; Ocampo, J.M.J.; Libardi, J.; Grigorov, K.; Massi, M.; Otani, C.; Ravagnani, S.P.; Maciel, H.S.; Guerino, M.; Ocampo, J.M.J.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)Mixtures of acetylene/argon and methane/argon with different volume percents of hydrocarbon were used as the precursor gas to grow DLC films, keeping constant the other process parameters. The substrates used were p-type (100) silicon wafers. The films were characterized by Raman spectroscopy, nanoindentation, atomic force microscopy (AFM) and by a profilometer. In order to grow DLC films with special properties that could make this material an alternative candidate for applications in micro-electromechanical systems (MEMS) production, a comparative analysis focused on the influence of the hydrocarbon precursor gas mixture on the mechanical and chemical properties of the DLC films is reported. © 2004 Elsevier B.V. All rights reserved.Ítem Improvement of performance in FFH-OCDMA systems by using strong apodized fiber Bragg gratings(SPIE-INT SOC OPTICAL ENGINEERING, 2004-01-01) Marulanda, JI; Torres, PI; Ramirez, CA; Marulanda, JI; Torres, PI; Ramirez, CA; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)This paper shows simulations of an all-fiber fast optical code division multiple access communications system (OCDMA), using strong apodized fiber Bragg gratings (FBGs) arrays as passive encoding-decoding devices. Auto and cross-correlation functions of the user signals, and bit error rate (BER) were used as evaluation criteria. Through numerical analysis, we demonstrated that when strong Bragg gratings are used the performance of the system is increased. We obtain the BER performance for strong gratings and compare results in various cases.